Research on the mechanism of granulosa cell luteinization using granulosa cell cultures in the rhesus monkey and pig will be continued. Gonadotropic (LH, FSH) control of cyclic AMP production, LH and FSH receptors, progesterone secretion, and morphological luteinization will be examined. During the past year we have demonstrated that FSH can stimulate LH-hCG binding in cultures of porcine granulosa cells obtained from small immature follicles. The ability of granulosa cells obtained from small porcine (1-2 mm) follicles to respond to FSH is greater than in the case of granulosa cells obtained from large (6-12 mm) follicles. The reverse is true in the case of LH and hCG in the rhesus monkey in vivo. The thecal cell of the prevulatory follicle is the principal source of ovarian vein estrogen. Bibliographic references: Channing, C.P. and F.L. Rigby. Methods for assessing hormone-mediated differentiation of ovarian cells in culture and in short term incubations. In: "Methods in Enzymology (J.G. Hardman and B.W. O'Malley, eds.), Academic Press, New York, 1975, vol. 39, part D, pp. 183-230; Tsafriri, A., and C.P. Channing, An inhibitory influence of granulosa cells and follicular fluid upon porcine oocyte meiosis in vitro. Endocrinology 96: 922-927, 1975.